1. Field of the Invention
The invention relates to a digital image processing technique. Particularly, the invention relates to an enlargement technique for a super-resolution image.
2. Description of Related Art
High resolution images can be applied to various domains including digital cameras, satellite images, medical images, surveillance video cameras and criminal investigations, etc. For example, the high resolution medical images help doctors to improve diagnostic accuracy and a surgical success rate. In application of the surveillance video camera, a tracking recognition rate is improved by enhancing a camera resolution, which may effectively provide the police more investigation clues.
Therefore, to enlarge a low resolution image to produce a high resolution image is always an important research issue in digital image processing, and image interpolation is a method related to an image enlargement technique. The image interpolation is generally implemented through single image enlargement, so that the image quality is greatly limited. For example, the commonly used signal image enlargement method includes polynomial interpolation, edge-directed interpolation and exampled-based for super-resolution.
Although the polynomial interpolation is simple and has a fast operation speed, the enlarged image is blurry due to lack of high-frequency information, and a block effect is generated. The edge-directed interpolation is to resolve the problem of the polynomial interpolation that the high-frequency information cannot be effectively presented. The high-frequency information refers to a texture and an edge region of the image, and this method focuses on preservation of the image edge, though a large amount of computations is required to accomplish the method. The exampled-based for super-resolution technique requires to establish a large high-low frequency corresponding database, and how to quickly find matched data from the large high-low frequency corresponding database is also a problem to be resolved.